Proton-acceptor ability of substituted pyridine N-oxides

The dipole moments and molar Kerr constants of H-bonded complexes of pyridine N-oxides with phenols were examined. Comparison of the dipole moments and molar Kerr constants of the complexes, obtained experi- mentally and calculated by additive schemes and by AMI and PM3 semiempirical methods, shows that the quantum-chemical methods used adequately describe the electrical properties of the complexes. It is shown that the logarithm of the equilibrium constants of complex formation fairly correlate with the charge on the oxygen atom of the N-O group of pyridine N-oxides. A method for estimation of the equilbrium constants of the first and second stages of complex formation was proposed. It is found that the polarity of the hydrogen bond correlates with the total charge on the H atom of the electron donor and the O atom of the proton acceptor.